1. Field of the Invention
This invention relates to devices and methods for performing nondestructive inspection on chips of semiconductor devices, and particularly to nondestructive inspection for detecting defects which are electrically active. This invention also relates to semiconductor devices, which are suited to the nondestructive inspection, and manufacturing methods of the semiconductor devices.
This application is based on Patent Application No. Hei 10-272788, Patent Application No. Hei 11-67744 and Patent Application No. Hei 11-133283 all filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, the nondestructive inspection techniques are disclosed by the known papers such as the paper entitled xe2x80x9cOBIC Analysis Technique By Thermo Electro-motive Forcexe2x80x9d, which is provided as the material for 132 meeting on study of 132 committee of Japan Academy Promotion Foundation with regard to industrial application of charged particle beams. Herein, xe2x80x9cOBICxe2x80x9d is an abbreviation for xe2x80x9cOptical Beam Induced Conductivityxe2x80x9d. The nondestructive inspection technique of this kind is used to nondestructively detect defect positions of wiring system in processes for defect analysis and fault analysis of semiconductor devices.
In addition, a variety of papers describe inspection of semiconductor devices and its related technologies using lasers. For example, the paper of Japanese Patent Application, First Publication No. Hei 7-14898 discloses OBIC analysis for semiconductor device wafers.
The paper of Japanese Patent Application, First Publication No. Hei 4-312942 discloses an OBIC current detection method for semiconductor devices.
The paper of Japanese Patent Application, First Publication No. Hei 5-136240 discloses OBIC observation for silicon semiconductor devices.
The paper of Japanese Patent Application, First Publication No. Hei 8-255818 discloses scanning-type OBIC current analysis using a scanning laser microscope.
The paper of Japanese Patent Application, First Publication No. Hei 10-170612 discloses inspection of defects in internal mutual wiring of semiconductor integrated circuits.
The paper of Japanese Patent Application, First Publication No. Hei 2-284439 discloses inspection of defects of semiconductor devices in manufacture of multilayer-wiring packages.
The paper of Japanese Patent Application, First Publication No. Hei 4-369849 discloses a semiconductor integrated circuit device, which is constructed to allow accurate measurement of electric potentials of aluminum wires located under oxide films.
The paper of Japanese Patent Application, First Publication No. Hei 5-47929 discloses automatic arrangement and wiring in layout designs of semiconductor integrated circuits.
The paper of Japanese Patent Application, First Publication No. Hei 5-243535 discloses design of semiconductor integrated circuits whose wiring patterns can be corrected with ease.
The paper of Japanese Patent Application, First Publication No. Hei 8-316281 discloses inspection of defects in patterns of multilayer wiring.
Now, FIGS. 8 and 9 show examples of configurations for the conventional device and method of nondestructive inspection (hereinafter, simply referred to as nondestructive inspection device and nondestructive inspection method), wherein same parts are designated by same reference symbols. A laser 1 generates a laser beam, which is narrowed down by an optical system 2 to produce a laser beam 3. Scanning is performed using the laser beam 3 on an observed area of a semiconductor device chip 4. The scanning is performed by polarization of the laser beam by the optical system 2 under control of a control image processing system 106.
In the above, an electric current is caused to occur and is extracted by a prober 115-1, which is subjected to probing to a bonding pad 14-1. The electric current is detected by a current variation detector 131 and is displayed on a screen of an image display device 7 under control of the control image processing system 106. Herein, variations of electric currents are displayed as an image representing luminance variations with respect to scan positions. Such an image is called a scan current variation image.
Concretely speaking, FIG. 8 shows an example of the configuration for the nondestructive inspection to let the current flow in a closed circuit. That is, a prober 115-2 is subjected to probing to a bonding pad 14-7, which is different from the bonding pad 14-1 connected to the current variation detector 131, and is grounded.
FIG. 9 shows an example of the configuration for the nondestructive inspection to let the current flow in an open circuit in a form of a transient current. So, all of bonding pads other than the bonding pad 14-1 connected to the current variation detector 131 are open. A capacitance (or capacity) component is required for the transient current to flow in the open circuit. In case of FIG. 9, such a capacitance component corresponds to a parasitic capacitance on the chip or a floating capacitance of a measurement system.
Next, operations of the nondestructive inspection will be described in detail. As described above, a difference between the configurations of FIGS. 8 and 9 merely lies in formation of the closed circuit or open circuit. So, the operations will be described without distinguishing between those configurations. Under the control of the control image processing system 106, the scanning is performed using the laser beam 3, which is originally generated by the laser beam generator 1 and is narrowed down by the optical system 2, on the observed area of the semiconductor device chip 4. Herein, the scan current variation image is subjected to illuminance display in response to the scanning in such a way that a current flowing into the current variation detector 131 is displayed xe2x80x9cbrightxe2x80x9d while its reverse current is displayed xe2x80x9cdarkxe2x80x9d, for example. Incidentally, the display is made using the contrast between light and shade as well as gradation.
When a laser beam is irradiated on a position in proximity to a defect, thermoelectroinotive force is instantaneously caused to occur so that a current flows in the aforementioned circuit. In contrast, when the laser beam is irradiated on a non-defective area, the thermoelectromotive force is not caused to occur so that the current does not flow in the circuit. Therefore, the image display device 7 displays an image (called a scan current variation image) in which the contrast between light and shade appears in connection with the position in proximity to the defect. At the same time when the scan current variation image is obtained, or just before or after the scan current variation image is obtained, a scan laser microphotograph is taken with respect to an optical reflected image, which emerges in connection with the laser beam scanning.
Then, the general-use image processing technique is used to perform composition on the scan current variation image and scan laser microphotograph to produce a composite image composed of two images. Using such a composite image, it is possible to clearly recognize a position corresponding to the contrast between light and shade in the scan current variation image, so it is possible to specify a defect position on the semiconductor device chip 4. Incidentally, the aforementioned technique has an accuracy in detection of the defect position in an order of submicrons.
In order to clearly detect a type of the defect and a cause of occurrence of the defect which is detected nondestructively as described above, physically destructive analysis is normally performed, using the focusing ion beam method or electron microscope method, on defect positions. In other words, the conventional technology is used to clearly recognize the defect positions with the accuracy in positional detection in an order of sub-microns, so it is possible to efficiently perform physical analysis on micro defects, sizes of which are under the sub-micron order. As described above, the aforementioned conventional technology plays an important role in a series of analytical procedures for the fault analysis and defect analysis.
Each of FIGS. 8 and 9 shows only one chip for simplification of illustration. Of course, probing operations similar to the foregoing one are performed when one of the chips arranged on a wafer is selected and inspected.
When the inspection is performed after completion of post-processes of manufacture in which the chip is enclosed in the package, a pin (or pins) of the package is used instead of the probing to establish an electric connection. In this case, it is the normal course of action to perform the inspection by removing the packaging material on the surface of the chip. For convenience sake, the description will be given by way of an example of a single independent chip, which represents the single chip, each of chips on the wafer and packaged chip, for example.
To clarify the description, an explanation is given with respect to a construction of the chip which serves as a model and its important points. FIG. 10 is a perspective view showing limited parts of a chip, which are relevant to the present invention. Important points of the present invention are provision (or non-provision) of bonding pads, electric connections derived from the bonding pads independently, and manners of the electric connections derived from the bonding pads independently.
A model chip shown in FIG. 10 has twelve bonding pads, which are designated by reference symbols of 14-1 to 14-12 respectively. Of course, the present invention is not necessarily limited by a specific number of the bonding pads. It is an important point of the-present invention to distinguish between a surface and a back of the chip. FIG. 10 clearly shows a surface 4f corresponding to formation of components on a semiconductor substrate but does not show a back 4b on which the components are not formed. Incidentally, a description will be given with respect to causes in which a distinction between the surface and back plays an important role in operations of the inspection.
FIGS. 8 and 9 do not specifically show the scanning mechanism of the laser beam and the scanning-related mechanism of the image display device, which are known arts. To avoid complication, the following description does not clearly refer to explanation with regard to some elements of the invention corresponding to the known arts.
However, the following description refers to relationships between the scanning of the laser beam and images being produced, which are important elements of the invention. Herein, the conventional art concerns with the relationship between the scan laser microphotograph and scan current variation image, while the present invention concerns with the relationship between the scan laser microphotograph and scan magnetic image. Incidentally, the scan current variation image and scan magnetic image differ from each other with respect to only the types of signals used for the basis of the display, while they are fundamentally identical to each other with respect to other factors. So, the following description will be given by way of an example of the scan current variation image.
FIGS. 11A to 11E are conceptual diagrams, which are provided to show a relationship between the scanning of the laser beam and produced images, wherein parts equivalent to those shown in FIG. 8 are designated by the same reference symbols. There are provided two kinds of the produced images, i.e., the scan laser microphotograph and scan current variation image. Herein, the scan laser microphotograph is produced as follows:
In synchronization with the scanning using the laser beams, reflected beams are detected from laser irradiated points, by which reflection intensities are displayed in luminance in response to points of the scanning to produce an image.
Incidentally, the scan current variation image is produced as described before. Both of the scan laser microphotograph and scan current variation image are produced simultaneously, or they are produced sequentially without moving the semiconductor device chip which serves as a sample. Thus, it is possible to obtain the scan laser microphotograph and scan current variation image with respect to a specific position of the semiconductor device chip.
Normally, the contrast between light and shade appears only at some part(s) of the observed area of the chip with respect to the scan current variation image. So, by displaying the scan laser microphotograph and scan current variation image which overlap with each other on the screen, it is possible to clearly display a position, at which the contrast occurs with respect to the scan current variation image, on the scan laser microphotograph with a high accuracy. This eases physical analysis of defects, which is performed after the nondestructive inspection.
FIG. 11A shows movement of a laser scan position 201 on the semiconductor device chip. FIG. 11D shows coordinates 202 of a luminance display position of the scan laser microphotograph, which is displayed in a scan laser microphotograph display window 204 (see FIG. 11C) on the screen of the image display device 7. FIG. 11E shows coordinates 203 of a luminance display position of the scan current variation image, which is displayed in a scan current variation image display window 205 (see FIG. 11C) on the screen of the image display device 7. FIG. 11B shows the laser scan position 201, which is scanned using the laser beam 3 on the semiconductor device chip 4.
FIG. 11C shows the aforementioned windows 204, 205, which are displayed on the screen of the image display device 7 in response to the scanning. Herein, a reference symbol xe2x80x9c7Axe2x80x9d shows the screen of the image display device 7, on which the scan laser microphotograph, display window 204 and the scan current variation image display window 205 are displayed.
Now, a description will be given with respect to relationships between the scanning of the laser beam, scan laser microphotograph and scan current variation image with reference to FIGS. 11A to 11E. Movement of the laser scan position 201 on the semiconductor device chip 4 starts at a start point 201-1, from which the laser scan position 201 moves along a first scanning line in a horizontal direction toward an end point 201-2, which corresponds to an end of the first scanning line. Such horizontal movement of the laser scan position 201 is repeated five hundreds and twelve times, for example. So, the laser scan position 201 lastly moves along a last scanning line from its left-end point 201-3 to its right-end point 201-4.
The aforementioned scanning is performed continuously from the start point 201-1 to the end point 201-4 on the screen. Such scanning is performed at one time, normally, in a time duration which ranges from 0.1 second to 10 seconds. In synchronization with the scanning, detection is performed on reflected beams of the scan laser microphotograph, while detection is performed on current variations with respect to the scan current variation image. As described before, the scan laser microphotograph is displayed using luminance values, which are produced by converting detected light intensities and are displayed on the basis of positional correspondence. In addition, the scan current variation image is displayed using luminance values, which are produced by converting the detected current variations and are displayed on the basis of positional correspondence.
To clarify the concept of the positional correspondence, a description will be given with respect to relationships between scan areas, image display areas and observation magnifications. A ratio (yd/xd) between a width xd and a height yd of a scan area should be maintained constant in a displayed image. So, a ratio (yr/xr) between a width xr and a height yr of a scan laser microphotograph is identical to the aforementioned ratio (yd/xd). Similarly, a ratio (yi/xi) between a width xi and a height yi of a scan current variation image is identical to the aforementioned ratio (yd/xd).
The observation magnification is expressed as a ratio (xr/xd) between the width xd of the scan area and the width xr of the scan laser microphotograph or a ratio (xi/xd) between the width xd of the scan area and the width xi of the scan current variation image. Normally, in order to overlap the scan laser microphotograph and scan current variation image together, they are produced in a same size. For this reason, the magnification (xr/xd) is identical to the magnification (xi/xd). In addition, the ratio (yd/xd) between the width and height of the scan area is identical to the ratio between the width and height of the image. So, the magnification is identical to (yr/yd) and (yi/yd) as well.
Next, a description will be given with respect to correspondence between a point on the scan area and a point of the image being displayed. In general, the laser scan, is performed in an analog manner or a digital manner. Normally, the image display is performed in a digital manner. So, each position is expressed using coordinates corresponding to each pixel position. In many cases, resolution for the image display is represented by xe2x80x9c(512 pixels)xc3x97(512 pixels)xe2x80x9d. So, the following description is made by way of an example in which the image display has a resolution of xe2x80x9c(512 pixels)xc3x97(512 pixels)xe2x80x9d.
The start point 201-1 of the laser scan in the scan area (see FIG. 11A) corresponds to a start point 202-1 of the scan laser microphotograph (see FIG. 11D) and a start point 203-1 of the scan current variation image (see FIG. 11E) respectively. Coordinates (0, 0) are set to the aforementioned start points of the microphotograph and image. In addition, coordinates (511, 0) are set to end points of the microphotograph and image, which correspond to the end point 201-2 on the first scanning line of the laser scan in its scan area. Similarly, coordinates (0, 511) are set to start points of the microphotograph and image, which correspond to the start point 201-3 on the last scanning line of the laser scan in its scan area. Coordinates (511, 511) are set to end points (i,e., 202-4, 203-4) of the microphotograph and image, which correspond to the end point 201-4 on the last scanning line of the laser scan in its scan area. Thus, the image display is performed using a number of pixels (i.e., 512xc3x97512=262, 144), which are designated by the aforementioned coordinates (0, 0), (1, 0), . . . , (511, 511). Brightness of each pixel being displayed is normally designated by eight bits, which provide 256 steps in gradation.
The nondestructive inspection of the chip, which is performed using the aforementioned scan current variation image, has a variety of problems, which will be described below.
A first problem is that inspection cannot be performed on the semiconductor device chip, which is an inspected subject, after pre-processes of manufacture are completed so that bonding pads are attached to the chip.
In order to detect current variations which occur due to irradiation of the laser beam, the conventional art requires that the inspection device must be electrically connected to the semiconductor device chip. For this reason, the bonding pads should be formed on the semiconductor device chip in advance.
A second problem is that even if the inspection is performed after formation of the bonding pads is completed so that post-processes of manufacture are completed, many work steps and much cost are required for preparation in establishing electric connections because of a great number of bonding pads to which a current variation detector is connected.
In order to detect a defect which exists in the chip, it is required that a wire (or line) on which such a defect exists is electrically connected to the current variation detector. Therefore, in order to certainly perform the inspection, it is required for a human operator to electrically connect the current variation detector to all of the bonding pads, each of which has a possibility that a thermoelectromotive current flows therethrough. As a result, a great number of work steps and much cost are required for the preparation in establishing electric connections between the bonding pads and current variation detector.
In the case where the inspection is performed using the configuration of the closed circuit, it is necessary to select a bonding pad to configure the closed circuit. Combinations of the electric connections which can be established increase in proportion to the square of the number of bonding pads. So, as the number of bonding pads increases, a number of the combinations of the electric connections becomes enormous. In order to perform preparation regarding the electric connections being established every time the type of the chip, which is an inspected subject, is changed with new one, it is necessary to provide specifically designed instruments, and it is necessary to change the electric connections. This increases a number of work steps and an amount of cost being required for the preparation.
Another problem that the conventional art cannot solve is incapability of detecting short-circuit defects. The conventional art may be capable of detecting the voids, foreign matters and disconnection of wires. However, it is incapable of detecting short-circuits between wires. It may be possible to indirectly detect the short-circuit defects if defects causing the thermoelectromotive force exist on the same wires on which the short-circuit defects exist. However, there is a very small probability in which two kinds of the defects exist on the same wire.
It is an object of the invention to provide a device and a method for nondestructive inspection, by which productivity and reliability of semiconductor device chips are improved.
It is another object of the invention to enable nondestructive and non-contact inspection being performed before formation of bonding pads of the semiconductor device chips in semiconductor manufacturing processes.
It is a further object of the invention to enable efficient nondestructive inspection being performed without selecting bonding pads after formation of the bonding pads.
It is a still further object of the invention to provide a semiconductor device and its manufacturing method, which allow the nondestructive inspection device and method to detect short-circuit defects.
It is a still further object of the invention to provide a semiconductor device which is capable of increasing duration that a current flows due to occurrence of thermoelectromotive force caused by irradiation of a laser beam in proximity to a defect. So, it is possible to ease detection of a magnetic field, and it is possible to reduce manufacturing cost of the semiconductor device, thus, it is possible to improve productivity and reliability in manufacture of the semiconductor device.
In a first aspect of the invention, there is provided a nondestructive inspection device (or method) which is basically configured such that a laser beam having a specific wavelength is irradiated on a surface (or back) of a semiconductor device chip to scan. Herein, the laser beam is narrowed down in an irradiation size and is irradiated on a defect position. Then, the defect position is heated to cause a thermoelectromotive current, which transiently flows in the semiconductor device chip and which induces a magnetic field. A magnetic field detector such as SQUID detects a strength of the magnetic field, which is converted to a luminance value. The luminance value is set as luminance at a certain display position on a screen so as to produce a scan magnetic field image. A scanning laser microscope produces a scan laser microphotograph. Then, a display device displays a composite image consisting of the scan magnetic field image and the scan laser microphotograph, which are overlapped with each other, on the screen. Using the displayed composite image, it is possible to perform inspection on the semiconductor device chip as to whether a defect exists or not before formation of bonding pads in a nondestructive manner. Incidentally, the wavelength of the laser beam is set at 1300 nanometer for producing the scan magnetic field image and is set at 633 nano-meter for producing the scan laser microphotograph, for example. In addition, it is possible to provide at least one current circuit (e.g., closed circuit or open circuit) extracted from the semiconductor device chip, wherein one end of the current circuit is electrically connected to a bonding pad. Thus, it is possible to perform detection on the strength of the magnetic field, induced by the current flowing across the current circuit, with good detection sensitivity. Incidentally, the SQUID is cooled down in temperature using liquid nitrogen. Further, the SQUID contains three detection coils, which are directed in three independent directions respectively.
In a second aspect of the invention, there is provided a semiconductor device wafer, which is suited to the nondestructive inspection and is configured to allow detection of a short-circuit defect without using additional electric connections. A thermoelectromotive force generator and its wires are formed on (or in) a semiconductor device wafer, wherein they are electrically connected to first-layer wires, which are formed in an insulating layer on a substrate. For example, the short-circuit defect lies between the first-layer wires. Now, a laser beam is irradiated on the thermoelectromotive force generator so that a thermoelectromotive current is caused to flow in a closed circuit along a current path, which is configured by the first-layer wires, short-circuit defect, thermoelectromotive force generator and its wires as well as vias. Due to the thermoelectromotive current flowing across the closed circuit, a magnetic field is induced and is detected by a detector, such as a SQUID. Then, the detected strength of the magnetic field is represented in luminance (brightness or color), by which a scan magnetic field image is produced and displayed on the screen of the image display device in accordance with the scanning of the laser beam. A scan laser microphotograph is produced based on reflected light simultaneously with the scanning of the laser beam or in connection with the scanning of the laser beam. A composite image, consisting of the scan magnetic field image and scan laser microphotograph which are overlapped with each other, is displayed on the screen, by which it is possible to specify a position of the short-circuit defect in the semiconductor device wafer.
In a third aspect of the invention, a nondestructive inspection is effected on a semiconductor integrated circuit, which is in an intermediate stage of manufacture before formation of bonding pads. Herein, the semiconductor integrated circuit is basically configured by a substrate, an insulating layer, a first-layer wire, a circuit via, an inspection via and a metal film, which is used for formation of a second-layer wire. On the substrate, the circuit via is provided to connect the first-layer wire and second-layer wire via the insulating layer. The inspection via is connected to the first-layer wire but is not connected to the second-layer wire. The metal film is formed on a relatively broad range of a surface area, which is broader than a region of the first-layer wire. In addition, a part of the first-layer wire corresponds to a thermoelectromotive force generating defect. When a laser beam is irradiated on a back of the semiconductor integrated circuit toward the thermoelectromotive force generating defect of the first-layer wire, a thermoelectromotive current is caused to occur and flows in a closed circuit, so that a magnetic field is induced. A detector detects a strength of the magnetic field, based on which defectiveness of the semiconductor integrated circuit is inspected. Because the nondestructive inspection can be performed on the semiconductor integrated circuit which is in an intermediate stage of manufacture, it is possible to feed back inspection results in early stages of manufacture. This contributes to improvements in productivity and reliability of the semiconductor devices. In addition, it is possible to reduce the total cost required for manufacture of the semiconductor devices.